Alkylation of hydrocarbons



June zo, 1944. v HAE'NSEL 2,351,609

ALKYLATION OF HYDROCARBONS Filed April 13, 1942 Patented June 20, 1944 ALKYLATTON or nrnnocAaoNs Vladimir Haensel, Chicago, Ill., assignor to Unlversai Oil Products Company, Chicago, Ill., a

corporation of Delaware Application April 13, 1942, Serial No. 438,756

6 Claims.

This invention relates to the alkylationy of isoparalilns with oleiins for the production of higher molecular weight isoparaiiinic hydrocarbons of gasoline boiling range whichv have high antiknock ratings and are, therefore, suitable for use as motor fuels.

The invention relates more specifically to a combination of interrelated steps whereby a hydrocarbon mixture comprising essentially paraffins and olens is treated to alter the relative proportions of isoparaiilns, norma1 paratllns, and olefins thereby producing a hydrocarbon feed of more suitable composition for the subsequent alkylation step.

In one specific embodiment my invention comprises the steps of subjecting an olefln-paraflin mixture to solvent extraction with a solvent having' a relatively high selectivity for oleiins, separating an olen-containing extract from a paraf-L fin-rich raflinate, subjecting said paraffin-rich raffinate to fractionation for the separation of norma1 parafiins from isoparaiiins, introducing said olefin-containing extract and anisoparaffin-rich fraction from said fractionation step into a solvent stripping zone wherein the dissolved hydrocarbons are separated from said solvent by the stripping action of said isoparailin-rich fraction, returning the stripped solvent to the extraction zone, subjecting the effluent hydrocarbon vmixture from said stripping zone comprising isoparailins and oleflns, to the action of an alkylating catalyst under alkylating conditions, separating hydrocarbon phase from the alkylation step, subjecting it to fractionation to separate gasoline boiling range hydrocarbons and a fraction comprising essentially isoand normal butanes, supplying a portion of the last named fraction into the first named fractionation step, and recycling another portion thereof to the alkylation zone.

A hydrocarbon mixture suitable for use in the alkylation of isoparamns with oletlns must normally meet the following requirements:

(1) The ratio of isoparaiiins to olefns must be relatively high, e. g., from about 3:1 to as high as 20:1 or, in certain cases, even higher. It is known that the tendency toward undesirable polymerization of the olens may be lowered and the selectivity of the alkylation reaction may be increased by maintaining this ratio at a high level. Various procedures well known to those skilled in the art have been adopted to aid ln maintaining large molar excesses of isoparaiiins within the reaction zone, but it is of fundamental importance that the combined hydrocarbon (Cl. 26o-683.4)

charging stock itself contain a substantial excess of isoparanins over olefins.

(2) The normal paraiiin content should be as low as possible. Normal paraiiins introduced into the alkylation zone with the fresh feed tend to pass through the system substantially unchanged under conditions at which isoparaflins alkylate readily. The n-paraflins act as diluentsand as such make it necessary to employ considerably larger reaction zones than would be required if they were not present. Furthermore, the presence of large amounts of norma1 parafflns such as n-butane, in the reaction products creates a diicult fractionation problem since the unconverted isoparafiins to be alkvlated are commonly separated from the reaction products and blended with the desired amount of fresh feed to form the combined hydrocarbon charge to the alkyla.. tion zone.

(3) 'I'he olefin content of the charge should not be below certain known economically feasible levels. Although a high isoparaffin to olefin ratio in the charge is used in order that the alkylation reaction may predominate over polymerization and other competing side reactions, nevertheless itis not usually feasible from a commercial point of view: to utilize a combined feed having an abnormally low olefin content. If the olefin content is very low, e. g., of the order of 1 to 3%, the yield per pass of alkylate willalso below and the cost of recycling large amounts o f hydrocarbons will be high. Therefore, it ls desirable from an economic standpoint to keep the olefin content of the combined feed above some rather arbitrarily dened minimum, e. g., 5 to 10%, .or in certain instances even higher. The exact olefin content used in any particular instance will, of course, depend 'on many factors such as the nature ofthe charging stock, catalyst, operating conditions, etc.

Ordinary refinery gases such as butane-butylene mixtures or other C4 fractions are commonly used as sources of fresh hydrocarbon feed to alkylation processes. Such fractions usually have relatively low isoparain to olefin ratios, e. g., of the order of 0.5:1 to 2:1, and are commingled with a substantial quantity of isobutane or an isobutane-rich hydrocarbon fraction to produce a combined feed of the desired isoparaiiin to oleiin ratio. Because of the molal excess of isoparaffin, a major portion thereof remains unallrylatedl in a single pass through .the reaction zone, and is subsequently recovered and commingled with additional quantities of the olefin-containing feed, and then recycled to the alkylation zone.

Ihus, it will be seen that a substantial quantity of isoparailn is recycled within the system for the purpose of maintaining a high isoparamn to olefin ratio in the combined feed, and is ultlmately alkylated.

By the process oi' my invention a fresh feed is treated in a combination of steps with the net result that the normal parailln content of the feed is substantially reduced. An important advantage thereby accrues since it will be readily seen that for two fresh feed stocks comprisv ing essentially only C4 hydrocarbons and having the same olefin content, the stock having the lower normal butane content will also have the higher ratio of isoparaffln to'olenn. Thus, in feed stock B, shown below, which contains only 9% normal butane, the isoparailln to olen ratio is 2.0 as compared with feed stock A which contains 36% normal butane and has only a 1.1 isoparailln to olefin ratio.

Feed stock But lene's mol percent 30 30 n-Btane.' as s l-Butane 33 60 C: hydrocarbons 1 l.

Isoparaflin/oleiin ratio 1.1 l 2.0

As a result of the higher initial isoparailln to normal paraflins apparently act largely as diluents at usual conditions for alkylating isoparaflins and their removal from the fresh feed effectively lowers the reactor size and fractionai tion requirements.

The reduction in fractionation requirements is of particular importance since separation of isobutane from normal butane is one of the most diicult and costly steps associated with alkylation processes. Moreover, it is impractical to ajttempt a removal of normal butane from a fresh butane-butylene feed stock by fractionation because the closeness of boiling points of the constituents results in a substantial loss of olens. 'I'he solvent extraction method of the present invention solves this problem and permits the economical rejection of normal parafllns from the system.

The invention becomes of considerable importance in cases where it is necessary to produce aviation fuels from available stocks of diverse character, many of which do not inherently meet the requirements. of a satisfactory alkylation feed. The process, for example, has particular merit in cases where it is desirable to alkylate directly the C4 reaction products from a butane dehydrogenation unit. A hydrocarbon mixture of this type may contain for example, 25% butylenes, 6% isobutane, and 69% normal butane. Another application of my process is in cases where the initial olen content of the fresh feed is too low for direct use in a commercial alkylation process.

The alkylation of isoparains with olens may be conducted in the presencel of a variety of catalysts including phosphoricacid, various active metal halides and hydrogen halides such as aluminum chloride and hydrogen chloride, aluminum bromide and hydrogen bromide. and the mally gaseous oleflns such as propylene and theV butylenes. The latter hydrocarbons are readily available in substantial quantities from the cracking of petroleum oils and fromthe natural gasoline industry.

The invention will be more fully understood from the following description read in connection with the accompanying drawing which shows a schematic flow diagram of one manner in which the process may be carried out.

The hydrocarbon fresh feed is introduced through line l into extraction zone 2, and a solvent having substantial selectivity for olens is introduced by means of line 3. The extraction zone may consist of a packed tower wherein the hydrocarbon charging stock is introduced at the bottom and passed upwardly in countercurrent flow to the solvent which is introduced at the top of the tower. Any suitable apparatus may be used for the extraction step, and several stagesof extraction may also be used. The solvent may be used as an absorbing or scrubbing liquid for removing oleflns from the gaseous hydrocarbon charge, but the extraction may also be carried out under sufficient pres- Vsure to maintain` substantially liquid phase conditions for both the hydrocarbons and solvent.

Various solvents having marked selectivlties for olelnic hydrocarbons may be used, but the preferred solvent is of the type which has a low solubility at ordinary temperatures and pressures but exhibits l-'a considerable solubilityA at higher pressures, for example, fromabout 50 to about 200 atmospheres, and at elevated temperatures between about and about 350 C. Among such solvents are water and dilute aqueous solutions of various oxygenor nitrogen-containing organic compounds which I have found to possess high selectivity for the olenic constituents of a paraffin-olefin mixture at the pre-` ferred conditions. In certain instances I have found it desirable to operate the extraction step above the critical temperature of the hydrocarbon solute since it has been observed that a use of these temperatures leads to considerable solubility withouta substantial decrease in selectivity.

A butylene-containing extract is removed through lineV I3 and passes to stripping zone I2. The residual butane-rich rafiinate isl withdrawn through line 4, and a portion thereof may be continuously recycled by means of line 5 to the extraction zone. If desired, the unrecycled railinate may be withdrawn from the system through line 4, but itis preferably introduced by means of line 6 to fractionation zone 1. If desired, a mixture of isoand normal butanes may be added -from an external source through line 8. Separation of the isoand normal butane is effected in fractionation zone 1 and the normal butane is rejected from the system through line l. The

isobutane is removed through line III and intro.

duced by means of line II into stripping zone I2.

'I'he following examples will illustrate the nature of the results which can be obtained by the rocess pf my invention, although it is not intended that the invention be unduly limited there- Zone I2 may comprise any suitable form of 5 by.' Data are presented from five runs using apparatus such as a packed tower, etc., wherein aqueous solutions of various organic compounds the solution of butylenes in the solvent is subas solvents in the extraction of butane-butylene iectcd to the stripping action of the isobutane mixtures. Runs 1, 2, and 3 were made with a stream. It will be apparent that the conditions charging stock having the following molal comof temperature and pressure in the/ stripping zone i position: 17.0%' i-CiHm; 51.8% n-CIHio; 11.8% and of the entering streams of extract and ison-C4He-1; 9.4% i-C4Ha; 0.6% Cs and heavier hybutane may be adjusted to obtain an effluent mixdrocarbons. The total olefin content of the ture which will have the desired olefin content. charging stock was 30.6%. Runs 4 and 5 were The stripped solvent is withdrawn by means of made with a similar hydrocarboncharging stock line 2l and is preferably recycled through line Il 1,5 in which the total olefin content amounted to to extraction zone 2. 'I'he mixture of isobutane only 23.7%.

Run No.

1 z e l 4 5 'remp.,c 18e iss 185 190 m4'. Press., atm 83 73 77 59 68. Per cent olellns in hydrocarbons dlssolved in extract :me 64.7 58.3 51.8 aac 36.5. Se ectivityratio 1...-- 4.16 3.17 2.44 2.20 1.90.

l This ratio is defined as the volume ratio of oleilns to parains in the extract phase divided by the same ratio in the hydrocarbon charge.

v tration, is introduced into the alkylation zone through line I1. The reaction mixture or emulsion passes through line I8 to separation zone I9 which may conveniently comprise a settling zone.

The catalyst layer is removed through line and a substantial portion thereof is recycled through line 2I tc the alkylation zone I6. A portion of the used catalyst is continuously withdrawn from the system through line 20. In the case of hydrogen fluoride catalyst, the used hydrogen fluoride withdrawn from the system may be regenerated readily and returned to the system through line I1.

An upper hydrocarbon layer is removed from separation zone I9 through line 22 and introduced into fractionation zone 23. In certain instances, an unconverted isobutane stream may be recovered through line 24 and recycled to the alkylation zone. To obtain the major benefits of my invention, however, the isobutane-normal butane stream containing largely isobutane is removed in fractionation zone 23 and recycled by means of line 25 to the alkylation zone I5, at the same time diverting a portion of this total butane stream through line in the first fractionation zone 1, in order to prevent the buildup of normalA butane in the alkylation sys-tem. This procedure avoids the diflicult and expensive fractionation oi' nand iso-butanes in zone 23, thereby cutting down on plant and operating costs.

Light gases may be recovered through line 28, a gasoline boiling range alkylate is removed through line 21, and the higher boiling products of the process may be recovered through line 20.

spectively. The` relative effectiveness of the several solvents employed is also reflected in the value of the selectivity ratio in each case.

The paraffin-rich raffinate in each case is fractionated to .separate isobutane which is then used as a stripping medium to strip or desorb the hydrocarbons from the solvent. Operating conditions in the stripping zone may be varied over a substantial range, but in general the pressure is preferably lower than the pressure inthe extraction zone. However, both extraction and stripping zonesmay be operated at approximately the same conditions of temperature and pressure if desired.

The eliluent hydrocarbon mixture from the stripping zone in each case has' a substantially lower normal butane content than the feed. This mixture is charged to a sulfuric acid or hydrogen fluoride alkylation process which may be operated at a temperature of 25 to 50 C. in the case of sulfuric acid and at about 10 to 100 C. in the case of hydrogeniiuoride catalysts. In either case, the pressure is preferably maintained high enough to insure substantially liquid phase operation. An isoparaflln to olefin ratio of from about 4:1 to about 20:1 is maintained in the alkylation zone by recycling a substantial quantity of isobutane within the system. Under these conditions, a yield of 300 F. end-point alkylate of the order of about 180 to 250 Weight per cent based on the oleflns charged may be obtained. This product is highly isoparaillnic and has an A. S. '1'. M. octane number of 93 to 95. During fractionation of the reaction products, a total unconverted butane mixture is separated and is recycled in part to the alkylation step. A side stream is continuously separated from this recycle stream and is subjected to fractionation in the railinate i'ractionator, as shown is the drawing, in order to prevent a build-up of normal butane within the alkylation system.

I claim as my invention:

1. A method for preparing a mixture rich in isoparamns and oleiinsfrom a hydrocarbon fraction containing the same and normal paramns which comprises extracting oleilns from the irac-V which comprises subjecting the i raction to the action `of an aqueous solvent ha g a relatively high selectivity for olenns at a temperature above the critical temperature of said olens to form an olen extract, fractionating the resultant paraiilnic raiiinate into a normal parain part andan isoparamn part, stripping the oleiin lextract of its oleilns by contacting the same with at least a portion of the isoparaiiin part and recovering the resultant isoparamn-olen mixture.

3. The process of claim 1 further characterized in that the solvent comprises an aqueous solution of an organic' solvent.

4. The process of claim 1 further characterized extract,

in that the solvent comprises an aqueous solution oi' methyl ethyl ketone.

5. A process which comprises subjecting a hydrocarbon fraction containing normal and isoparamns and olens to the action of an aqueous solvent having a relatively high selectivity for the olens to form an oleiin extract, fractionating the resultant parailin rafiinate into a normal paraiiin part and an isoparain part. stripping the olen extract of its olens by contacting the same with at least a portion of said isoparailln part, subjecting the resultant isoparamn-olein mixture to alkylation and react-y ing the isoparains with the olens, separating unconverted parains from the resultant reaction products and supplying at least a portion oi' :ad unconverted parailns to the fractionating 6. A process which comprises subjecting a C* fraction containing butanes and butenes to the action of an aqueous solvent having a relatively high selectivity for the butenes to form a butene fractionating the resultant butane ramnate into a normal butane fraction and an isobutane fraction, stripping the butene extract of its butenes by contacting the same with at least a portion of the isobutane fraction, subjecting the resultant isobutane-butene mixture to akylation to react the isobutane and butenes, separating unconverted butanes from the resultant reaction products and supplying at least a portion of the unconverted butanes to the fracl tionating step. 

